Add support for xz compressed packages

[ngetahun]

Description

This PR attempts to add support for xz compressed debian/fedora repositories.

• Related Issue / Ticket / Trello card:

How to test

• Use docker compose to launch rmt

> docker-compose up --build -d

• Run bash in rmt container

> docker-compose exec -it rmt bash

• Add the following deb repo as a custom repo

> bin/rmt-cli repos custom add https://security.debian.org/debian-security/dists/bullseye-security/contrib/binary-all/ deb_xz

• Mirror the repo

> bin/rmt-cli mirror repository deb_xz

Change Type

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• Bug Fix (a non-breaking change which fixes an issue)
• New Feature (a non-breaking change which adds new functionality)
• Documentation Update (a change which only updates documentation)

Checklist

Please check off each item if the requirement is met.

• I have reviewed my own code and believe that it's ready for an external review.
• I have provided comments for any hard-to-understand code.
• I have documented the MANUAL.md file with any changes to the user experience.
• If my changes are non-trivial, I have added a changelog entry to notify users at package/obs/rmt-server.changes.

Review

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[digitaltom]

@ngetahun @arharovets I think we're missing xz support for repomd repositories which were the original request (https://bugzilla.suse.com/show_bug.cgi?id=1246976)

[arharovets]

@ngetahun @arharovets I think we're missing xz support for repomd repositories which were the original request (https://bugzilla.suse.com/show_bug.cgi?id=1246976)

opened a follow-up: #1385